Inkjet type printers typically employ a print cartridge that is moved in a transverse fashion across a print media. Contemporary disposable inkjet print cartridges typically include a self-contained ink container, a print head including a plurality of inkjet nozzles in combination with the ink container, and a plurality of external electrical contacts for connecting the inkjet nozzles to driver circuitry in the printer. Failure of a disposable print cartridge is usually related to electrical damages to the resistors used to vaporize the ink and eject droplets from the nozzles. As inkjet technology has improved, the reliability of the print cartridge has improved dramatically. The print head assemblies used in the contemporary disposable inkjet print cartridges are fully operable to their original print quality specifications after printing ink tens or even hundreds of times the volume of the self-contained ink container.
Efforts have been pursued in the inkjet industry to extend the lives of the print cartridges in printers to reduce the cost of operation and to reduce the frequency of cartridge replacement for customers, as well as for environmental reasons. Print cartridge life can be extended by merely making the cartridge container larger in size such that it can hold a larger ink supply. But this approach adds extra weight on the printer carriage, which moves side to side continuously across the media width for image printing. The extra weight on the carriage causes more mechanical stress to the printer structure and demands a larger motor to drive the carriage.
U.S. Pat. No. 5,686,947 to Murray et al., discloses a wide format inkjet printer which provides a substantially continuous supply of ink to a print cartridge from a large, refillable ink reservoir mounted within the printer. Flexible tubing, permanently mounted within the inkjet printer, connects the reservoir to the print cartridge. The off-carriage ink supply allows a print cartridge to function for the full cartridge life while eliminating the problems related to the extra weight on the carriage of an on-carriage large ink supply. An on-carriage ink refill system is provided by U.S. application Ser. No. 10/138,883, filed on May 3, 2002. A replaceable ink container is installed onto the print cartridge. As ink in the print cartridge is depleted from the nozzles, ink in the replaceable ink container is drawn to the cartridge through an anti-siphon tube built inside the container. When the container is about out of ink, it is removed and replaced with a new ink container.
For both ink delivery systems mentioned above, diligence is necessary for the operator of the printer to inspect the refillable ink reservoir or to replace the replaceable ink container, and to ensure that they are not out of ink before refilling or replacement. Running out of ink may result in catastrophic print cartridge failure due to cartridge running dry or image printing failure due to ink starvation. Therefore, it is desirable if the printer can automatically sense the ink presence in the ink delivery system to avoid the failures.
U.S. Pat. No. 5,079,570 by Mohr et al. discloses a transparent vertical ink tube attached to a cartridge housing filled with foam. The capillary effect of the foam to ink causes the tube to be empty of ink when the ink level in the cartridge goes below a certain level. Therefore, the out of ink state can be detected visually or by instrumentation. U.S. Pat. No. 5,386,224 by Deur et al. places an ink level sensing probe into the ink supply tank to sense ink presence through the electrical conductivity of the ink. U.S. Pat. No. 4,639,738, by Young et al. and assigned to the common assignee of the present invention, discloses a detection system which incorporates detection ports in the cartridge for detecting pressure difference in the top and the bottom of the cartridge using a pressure differential sensor that signals a refill condition. U.S. Pat. No. 5,616,929 by Hara discloses an ink tank having an inclined interface, which selectively reflect the incident light from a light source depending on if there is ink presence or no ink presence in the tank. When no ink is present, the incident light is totally reflected and can be visually observed.
The application of a light source is advantageous because the light can be easily sensed automatically and the majority of the sensing components can be made not in contact with ink. U.S. Pat. No. 6,302,503 by Seu discloses a cartridge filled with glass beads. A light source illuminates the beads through a transparent window and a photo sensor records the reflected light. As the ink level drops below the level of the sensor, the recorded intensity of the reflected light shows a difference. U.S. Pat. No. 6,554,381 by Locker et al. provides a reflection body floating in a fluid receptacle. When light from a light source is directed to the reflection body, it is reflected back and received by a light detector. The fluid level causes variable amount of light being detected.
U.S. Pat. No. 5,689,290 by Saito et al. employs a phototransistor to sense the light transmitted through an ink chamber to detect ink presence. Another transmissive sensing system is disclosed in U.S. Pat. No. 6,247,775 by Walker. These transmissive approaches generally rely on the difference of light absorption between ink and air. The light intensity needs to be measured against a threshold to determine the ink presence.
U.S. Pat. No. 5,997,121 by Altfather et al., U.S. Pat. No. 6,234,603 by Altfather et al., U.S. Pat. No. 6,409,302 by Altfather et al., U.S. Pat. No. 6,494,553 by Donahue et al., U.S. Pat. No. 6,520,612 by Merz et al., all assigned to Xerox Corporation, and U.S. application Ser. No. 09/792,980 filed on Feb. 26, 2001 by Altfather et al. from Xerox Corporation involve different applications of an ink sensing apparatus which comprises a light source, a photosensor and a faceted prism inside a transparent wall of an ink container. When the prism is exposed to air, the light directed from the light source to the prism is internally reflected by the facets back to the photosensor. When the prism is immersed in ink, weak light is reflected back to the photosensor.
U.S. Pat. No. 6,361,136 by Watanabe et al. and U.S. Pat. No. 6,443,546 by Takagi, both assigned to Canon Kabushiki Kaisha, also involve faceted prism means for reflecting light to detect ink presence inside the container. The application of a faceted prism magnifies the light signal difference between ink presence and no ink presence in the ink container. Such a sensing system may not be universal to all liquids. For example, a reflective liquid may cause malfunction of sensing.